So you mean that with such a prop that never stalls you may increase the thrust as much as you want provided you can get enough rpm? Where is the limit?
Yes. The limit comes from compressibility effect when the speed of the propeller blades approaches speed of sound in which case drag increases dramatically and efficiency falls off rapidly. I haven't seen any experimental data for thrust (Ct) and power (Cp) coefficients for propellers operating at supersonic speeds. That would be really interesting.
Of course, mechanical strength may also be a consideration.
/Red B. (back on-line tomorrow)